1. Field of the Invention
The present invention relates to a detector for detecting rotation of a rotating body such as an internal combustion engine.
2. Description of Related Art
An example of a conventional detector for detecting rotation of a rotor made of a magnetic material is shown in FIGS. 14-16. A sensor chip 101 composed of a pair 1 of magnetoresistive elements (MRE 1 and MRE 2) and another pair 2 (MRE 3 and MRE 4) is positioned to face the rotor RT made of a magnetic material and having projections formed around its outer periphery. The sensor chip 101 is integrated with a circuit for processing outputs from the sensor chip 101 and is molded with resin 102. The sensor chip 101 is electrically connected to terminals T1, T2 and T3 at an inside of the molded resin 102. The terminal T1 is a terminal for supplying electric power to the sensor chip 101, the terminal T2 is a terminal for leading out output signals from the sensor chip 101 and the terminal T3 is a ground terminal. A magnet 30 for supplying a biasing magnetic field to the sensor chip 101 is disposed around the sensor chip 101. In other words, the sensor chip 101 is disposed in a hollow space 31 formed in the magnet 30.
The sensor chip 101 molded with the resin 102 and the magnet 30 are contained in a housing to form a unitary detector unit which is mounted on an engine, for example. Such a detector unit contained in a housing 120 is shown in FIG. 15. In FIG. 15, the same or similar components as those shown in FIG. 14 have the same reference numbers. As shown in FIG. 15, the molded resin 102 and the magnet 30 are contained in a cylindrical cap 40 having a closed bottom end, and the cap 40 is molded with a resin material that forms a housing 120. The housing 120 has a flange 123 for mounting the detector unit on an engine and a connector 124 in which metallic terminals 100a, 100b, 100c are contained. The terminals T1, T2 and T3 are connected to the metallic terminals 100a, 100b and 100c, respectively.
The rotor RT is made of a magnetic material, and projections are formed on the outer periphery of the rotor. As the rotor RT facing the detector unit rotates, a magnetic field formed by the biasing magnet 30 in the MREs 1-4 changes. Electrical resistances in the MREs 1-4 change according to changes in the magnetic field. Rotation of the rotor RT is detected as the resistance changes in the MREs 1-4. Outputs form the sensor chip 101 representing rotation of the rotor is fed to a circuit for processing the output signals, and the processed signals are led out through the output terminal T2 and are fed to an electronic controller (not shown).
The conventional detector unit described above is manufactured in the following manner. The molded resin 102 including the sensor chip 101 therein, the magnet 30 and the cap 40 are separately prepared. Then, these components are assembled and molded together, thus forming the housing 120. Since these components 102, 30 and 40 have respective dimensional deviations, there is a certain deviation in a position of the magnet 30 relative to the MREs.
FIG. 16 shows a schematic cross-sectional view of the detector unit, taken along line XVI-XVI shown in FIG. 15. Due to the dimensional deviations of the respective components, gaps d1 and d2 are formed between components as shown in FIG. 16. When these components are molded together into a unitary unit, forming the housing 120, a position of the sensor chip 101 relative to the magnet 30 includes a certain dimensional deviation. It is impossible to exactly position the sensor chip l01 relative to the magnet 30. Detection accuracy of the detector unit is adversely affected by the deviation of the position of the sensor chip 101 relative to the magnet.
JP-A-9-5017 proposes a structure of a rotation detector, in which accuracy in a relative position between a sensor element and a biasing magnet is improved. In this detector, a substrate carrying a Hall element thereon is directly mounted on a housing so that the Hall element correctly faces a biasing magnet which is also mounted on the housing. However, it is unavoidable to eliminate a certain deviation in a relative position between the Hall element and the biasing magnet because both components are mounted on respective surfaces of the housing which are apart from each other.